A general method for preparing a stable immunogenic product comprising antigenic heterocomplexes comprising one or more antigenic proteins of interest and at least one carrier protein has been described in the PCT application published under no WO 2004/024189 in the name of NEOVACS. Notably, said PCT application disclosed a method for preparing such heterocomplexes using TNFα as the antigen of interest and KLH as the carrier protein. Said general prior art method, when carried out for preparing heterocomplexes comprising TNFα and KLH, comprised the following steps:                a) obtaining a mixture of KLH with TNFα;        b) adding to said mixture glutaraldehyde at a final concentration of 0.026 M;        c) removing excess glutaraldehyde by performing a dialysis;        d) adding formaldehyde to the dialyzed solution and maintaining the presence of formaldehyde during a period of time of 48 hours;        e) adding glycine to the solution obtained at the end of step d); and        f) performing a dialysis with the solution obtained at the end of step e).        
The examples of the PCT application no WO 2004/024189 showed that the resulting TNFα/KLH immunogenic product was stable and able to raise the production of antibodies which possess a good neutralizing activity against native TNFα.
However, with time, it appeared that more efficient heterocomplexes were needed in view of satisfying the high level of requirements from the various Health authorities, including in the United States and in Europe, for the purpose of manufacturing suitable vaccine compositions containing said heterocomplexes as the main active ingredient.